1. Field of the Invention
The present invention relates to an optical recording medium-manufacturing apparatus that manufactures an optical recording medium by punching a central hole through a disk-shaped substrate.
2. Description of the Related Art
In general, when an optical recording medium (optical disk), such as a CD or a DVD, is manufactured, a thin film, such as a light-reflecting layer, is formed on a disk-shaped substrate having grooves and lands formed in a surface thereof by injection molding, and then a resin layer as a protective layer is formed on the thin film by the spin-coating method such that the protective layer covers the thin film. Further, when a writable optical recording medium, such as a CD-R, a CD-RW, a DVD-R, or a DVD-RW, is manufactured, thin films, such as a light-reflecting layer and a recording layer, are sequentially formed on a surface of a substrate, and then a resin layer as a protective layer is formed on top of the thin films by the spin-coating method such that the protective layer covers the thin films. If the optical recording media thus manufactured has variation in the film thickness of the resin layer thereof, it is difficult to reliably prevent damage from occurring to the thin film(s). Therefore, in the formation of a resin layer, it is necessary to spin-coat the entire surface of a substrate with a resin material for forming a resin layer, to a uniform thickness. Further, to form a resin layer having a uniform thickness on a substrate by the spin-coating method, it is preferable to drop a resin material onto the center of a substrate being rotated. However, it is necessary to form a central hole in the center of an optical recording medium, for enabling clamping (chucking) e.g. by a recording and reproducing apparatus, which makes it difficult to drop a resin material onto the center of a substrate during execution of spin-coating operation. To overcome this problem, the present inventors have proposed, in Japanese Patent Application No. 2002-196415, an optical recording medium-manufacturing apparatus (hereinafter also referred to as the “manufacturing apparatus”) which is configured to drop a resin material onto a substrate before forming a central hole, thereby forming a resin layer with a uniform thickness, and then punch the central hole such that the central hole extends through the substrate and the resin layer.
In the proposed manufacturing apparatus, first, an information-recording surface of a disk-shaped substrate (substrate) having no central hole formed in a central portion thereof is spin-coated with a resin for forming a light transmission layer. In this case, differently from the CD and the DVD of the type referred to hereinabove, an optical recording medium manufactured by the manufacturing apparatus proposed by the present inventors is configured such that in recording or reproducing record data, a laser beam is caused to enter the medium from a front surface side of a resin layer formed on a thin film. Therefore, in the manufacturing apparatus, when the optical recording medium is manufactured, a light transmission layer for transmitting a laser beam therethrough is formed in place of the protective layer in the above example. More specifically, an ultraviolet-curing resin, for example, is dropped onto the center (portion to be formed with a central hole afterwards) of a substrate being rotated by a coating device such that the resin material is caused to expand toward the periphery of the substrate by centrifugal force generated by rotation of the substrate. In doing this, the rotational speed of the substrate is properly adjusted, whereby the resin material is uniformly coated on the entire information-recording surface. Then, an ultraviolet ray is irradiated onto the resin coated on the substrate such that the resin is cured to form a light transmission layer.
Then, a circular cut having a diameter approximately equal to that of the central hole is formed in the light transmission layer in an area of the light transmission layer where a central hole is to be formed. More specifically, the substrate is rotated in a state where a blade of a tool is pushed into the light transmission layer, whereby a cut having a depth approximately equal to the thickness of the light transmission layer is formed in the light transmission layer. Subsequently, the substrate is transferred by a transfer mechanism from a processing location for forming a cut (hereinafter also referred to as the “cut-forming location”) to a location for forming a central hole (hereinafter also referred to as the “central hole-forming location”). Then, a hollow cylindrical punching tool is pushed into the substrate from the side where the light transmission layer is formed, to thereby punch a central hole. In doing this, since the cut has been formed in the light transmission layer prior to punching the central hole, peeling-off or formation of burrs is prevented from occurring to the light transmission layer during formation of the central hole. By carrying out the steps described above, the optical recording medium is completed. Thereafter, the optical recording medium is transferred by the transfer mechanism from the central hole-forming location to a stack location for stacking completed optical recording media.
However, from the study of the proposed manufacturing apparatus, the present inventors found out the following points for improvement: In the proposed manufacturing apparatus, a central hole is formed by moving a punching tool in the direction of thickness of a substrate to push the tool therein (pressure cut). Therefore, when the central hole is formed, a considerably large force is applied to the substrate in the moving direction of the punching tool, so that there is a fear of a central portion or its vicinity being partially broken before the cutting edge of the punching tool reaches the reverse side of the substrate (before the central hole is punched out). It is desirable to avoid this inconvenience. For this purpose, there has been conventionally proposed a method of smoothly pushing the tool (blade) into the object to be cut while causing ultrasonic vibration of the tool. This method enables the punching tool to be smoothly pushed into the substrate. However, the ultrasonic vibration of the punching tool makes it difficult to position the punching tool with respect to the substrate, so that there is a fear of an central hole being formed off-center with respect to the substrate. Further, in the manufacturing apparatus proposed by the present inventors, the substrate can be moved away by being caught by the punching tool when the punching tool is pulled out from the substrate after completing formation of the central hole, or can be moved together with a punched piece that is punched off from the substrate when the punched piece is removed. Hence, improvement in this point is desired.